Rocket propellants, motors and their manufacture



United States This invention relates to rocket propellants which contain a polymeric petrin acrylic ester which functions as a combined fuel, oxidizer, and structural component to thereby provide said propellant with physical strength, without need for supplemental energy-supplying ingredients to compensate for loss of energy from burning the said structural component. In another aspect this invention relates to rocket propellants containing a petrin acrylic ester as a combined fuel, oxidizer and structural component in a high and unpredicted state of uniformity of distribution to provide ballistics in an improved degree of reproducibility. In another aspect this invention relates to a casting method for manufacture of the abovedescribed propellants, wherein improved uniformity of distribution of said polymeric ingredient with concomitant improved ballistics is obtained, by uniformly mixing a monomeric petrin acrylic ester with the remainder of the propellant ingredients to form a solution in said monomer and then polymerizing the monomer durin curing to form said polymeric ingredient. In another aspect this invention relates to manufacture of the above propellants by solution casting as distinguished from slurry casting of the prior art, wherein there can be no settling out of ingredients during casting so as to thereby assure uniformity of distribution of ingredients necessary for optimum ballistics. In another aspect this invention relates to propellant motors wherein the propellant contains a polymeric petrin acrylic ester as a combination of fuel, oxidizer and structural components and wherein the propellant is strongly case bonded by penetration of said polymeric ester into a plastic layer, adhered to the chamber wall as a liner therefor, as an integral part of said liner.

Propellan'ts utilized in jet propulsion, as distinguished from air breather engines which carry their own fuel but rely on the surrounding atmosphere for oxygen, carry their own fuel and oxidizer components so as to be operable independently of the environment in which they are utilized, the fuel component functioning in most instances, in solid propellants, as a structural ingredient for imparting required physical strength to the propellant body.

For a number of years solid rock propellants utilized have been nitroglycerin-nitrocellulose double base compositions which have been manufactured in accordance with well known casting methods involving use of casting powder-casting solvent systems, these methods being utilized in the manufacture of large grains in lieu of the older and well lmown solvent and solventless methods which are limited in their applications to solvent removal and extrusion problems respectively, inherent with the manufacture of grains larger than about 6 to 10 inches in diameter.

In accordance with further work in the propellant field composite type propellants have been developed and consist of an oxidizer such as ammonium perchlorate and an organic binder and/or aluminum. These compositions are generally made by m xing all ingredients as a slurry and then slurry casting the ingredient mixture.

Propellant casting involves admixing the fuel and oxidizer components together with the remaining ingredients in measured proportions to form a mixture for casting which is then cast in a suitable mold to form atent ice the desired grain configuration. In slurry casting, the propellant ingredients are mixed as a slurry generally outside the mold and then poured into the mold for casting and retained in the mold under necessary time and temperature conditions to effect cure. Slurry casting is often applied in manufacture of a propellant motor by pouring the slurry of propellant components directly into the motor chamber for casting and curing. In the use of a casting solvent-casting power system, the casting powder is positioned in the mold and the casting solvent is separately introduced into the mold and passed through the powder to fill the void spaces therein and to cause the grains of powder to coalesce into a unitary mass of plastic composition. One embodiment of that method involves placing the casting powder in the mold and passing the casting solvent upwardly through the body of powder to fill the voids to provide the coalesced mass for curing.

In the manufacture of many rocket motors, it is absolutely required that the propellant be bonded to the inner wall of the motor chamber during handling and firing, otherwise burning takes place along the grain on the surface adjacent the fissure to thereby disturb the burning equilibria and greatly impair the ballistics. Further, a strong case bond lends great structural support to the propellant during handling and firing.

Impaired ballistics also result when the ingredients of the propellant are not uniformly mixed. It is, therefore, important that a propellant be manufactured under conditions which maintain uniform distribution of all ingredients throughout the propellant. Propellants also require physical strength in order that they resist deformation of grain configuration during handling and storage, and Withstand the pressure load imposed during firing in order to provide the required ballistics. Structural ingredients are, therefore, employed to impart the'necessary strength to the propellant for resisting such physical failures. However, it is also important that the propellant be sufficiently flexible so as to adequately compensate for the difference in coefficient of expansion of chamber and propellant without incurring grain fracture or failure of the case bond.

In any propellant preparative method, there is always the problem of obtaining uniform mixing of the ingredients, inasmuch as nonuniform ingredient distribution results in uneven burning and impaired ballistics. Accordingly, the fewer ingredients in the propellant, the less is the possibility that such uneven ingredient distribution will occur.

Another problem often encountered in the solid propellant field is that of cold flow of the propellant which, as is well known, is the gradual flow or sagging of the grain to alter its configuration with concomitant impairment of ballistics.

For many propellant applications it is necessary that long burning times be sustained so that it is of importance that propellants of low burning rates be provided for that purpose.

This invention is concerned with new rocket propellants which contain a polymeric ingredient which functions as a combination of fuel, oxidizer and structural components to provide maximum uniformity of ingredients distribution, which are characterized by lowered burning rates, which exhibit high resistance to cold flow, which can be strongly case bonded, and which are sufficiently flexible as to maintain the case bond during handling and firing and to withstand operating pressure during said firing without incurring grain fracture. The invention is further concerned With a method for manufacture of the propellants, which initially incorponates the polymeric ingredient into the formulation in monomeric form to provide propellants characterized as above described. Fur- 100 hours.

ther, the invention is concerned with propellant motors containing the above described propellants strongly case bonded with the inner chamber wall.

In accordance with the invention a method is provided for incorporating a structural ingredient into a solid rocket propellant in improved degree of uniformity of distribution while also supplying energy with the said ingredient, the said propellant being formed only from ingredients which are soluble with a monomeric petrin ester described hereinafter to form a true solution, which method comprises forming a solution of at least one monomeric petrin ester selected from the group consisting of petrin acrylate and petrin methacryl'ate, and the remainder of the ingredients for forming said propellant, and casting the resulting solution and curing same at a temperature sufliciently high for a time duration suiticiently long to polymerize at least a portion of said ester. Further in accordance with the invention a solid rocket propellant is provided, formed by admixing a monomeric petrin ester only with propellant ingredients soluble therewith, to form a true solution, followed by casting the resulting solution and curing the cast solution for a time sufficiently long at a temperature sufiiciently high as to polymerize at least a major portion of said monomer, whereby a polymeric ester is provided as a combined fuel, oxidizer and structural ingredient, said ester being selected from the group consisting of petrin acrylate and petrin methacrylate. Still further in accordance with the invention a rocket motor is provided wherein the inner Wall of the motor chamber is lined with a layer of plastic material adhered thereto, and wherein the propellant is solid and contains a polymeric petrin ester selected from the group consisting of petrin acrylate and petrin methacrylate, and only as remaining ingredients, those which are soluble with said ester when in monomeric form to form a true solution, and wherein the propellant is bonded to the chamber wall by a continuous phase of said polymer extending across the propellant liner interface from the propellant into the said liner. 7

In accordance with a now preferred method embodiment, a solution of the propellant ingredients is made up inside the mold and retained in the mold under the necessary time and temperature conditions to effect curing. Generally the mold is the motor chamber of a rocket structure. The acrylate or methacrylate, or both if desired, are added in monomeric form and polymerized during the curing to form the polymeric ingredient which functions to supply structural strength and also as a combined fuel and oxidizer compound. Exemplary ingredients, all soluble in each other to form a true solution, are, on a weight basis, about 30 to 95 percent petrin acrylate or methacrylate or a mixture of these two esters; about 1 to 10 percent of a cross-linking comonomer such as divinylbenzene, glycol diacrylate, diglycol dimethacrylate, which are now preferred; from 0.1 to 2 percent of a polymerization catalyst such as benzoyl peroxide or t-butyl perbenzoate being now preferred; from 0.2 to 2 percent of a stabilizer such as ethyl centralite, nitrodiphenylamine, and fi-nerolin; and from 10 to 50 percent of a supplemental oxidizer, preferably nitroglycerin or nitrocellulose, the latter in limited amount as described hereinafter.

The ingredients are admixed in any desired order to form the solution at temperatures not exceeding about 70 C. but sufiiciently high that the petrin ester dissolves with the remaining ingredients to form the solution, which is above about 50 C. Mixing time depends to some extent upon the specific mixing apparatus utilized, generally varying from about 10 to about minutes. The solution is then cast into a mold for curing for about to The solution is maintained generally at a temperature of from about to 'C. over the 40 to hour curing period although these time and temperature conditions can be varied dependent upon the particular solution being cured. Polymerization of the monomeric petrin ester during curing is in some instances in complete, there generally being in such cases in the order of about 10 to 15 percent monomer, that remains unpolyrnerized. The remaining unpolymerized material serves as a plasticizer and oxidizer but contributes no strength.

The monomeric petrin ester ingredient is advantage ously utilized together with a monomer copolymerizable therewith to provide a resulting copolymer as the structural ingredient upon carrying out the in situ polymerization of the casting method of the invention. Mole ratios of such comonomer to monomeric petrin ester are as high as lzl although generally lower, say, in the order of about 0.711 and lower. The in situ copolymerization conditions are the same as those employed when the petrin ester is polymerized as above described. Exemplary comonorners polymerizable with the petrin ester monomer to provide a copolymer as the structural ingredient are: vinyl ethers, vinyl esters, allyl esters, alkyl and aryl sorbates, alkyl and aryl maleates, aryl acrylates, aryl methacryletes, alkyl methacrylates and alkyl acrylates; and specific cornonomers including glycerol dinitrate acrylate, glycerol dinitrate metliacrylate, erythritol trini trate methacrylate, erythritol trinitrate acrylate, trinitroethyl acrylate, trinitroethyl methacrylate, methyl acrylate, methyl methacrylate, butyl methacrylate, butyl acrylate, vinyl acetate, butyl maleate, vinyl butyl ether, styrene, acrylonitrile, vinylidene cyanide, butadiene, isoprene, vinyl ethyl ether, petrin maleate and chloroprene.

The comonomer ingredients above exemplified are not to be confused with the cross-linking comonomers described herein, these latter ingredients serving to copolymerize with the'monomeric petrin ester to cause the resulting polymer to be branched instead of straight chain, independently of whether the polymer, so cross-linked, is a. copolymer or is a product of polymerization of the petrin ester alone.

As herein illustrated, although supplemental oxidizers, stabilizers and cross-linking agents are advantageously in combination in many formulations, it is not necessary that all three be present in all instances. Cross-linking agents are advantageously employed when it is desired to impart maximum resistance to cold flow. The crosslinking agent, i.e., cross-linking comonomer, functions to react, i.e., copolymerize, with the petrin ester monomer to provide branching of the otherwise substantially linear polymer or copolymer. The propellant particularly with cross-linking agent as an ingredient, shows, after curing, no cold flow over periods of several days after which time in some instances there may be an elastic deformation or sag corresponding to an elongation of up to about 3 percent above which no appreciable further extension occurs at stress levels of the order of 2 p.s.i. or less. Further exemplary of cross-linking monomers utilized in the practice of the invention are vinyl acrylate, vinylmethacrylate, vinyl sorbate, and vinyl maleate; pentaerythritol dinitrate diacrylate, pentaerythritol dinitrate methacrylate, pentaerythritol 'mononitrate triacrylate, alkyl and aryl diacrylates, allryl and aryl dimethacrylates, alkyl and aryl triacrylates, alkyl and aryl trimethacrylates, glycol dimethacrylate, polyethylene glycol dimethacrylate, polethylene glycol diacrylate, polypropylene diacrylate, polypropylene dimethacrylate, epichlorohydrin dimethacrylate, epichlorohydrin cliacrylate, polytetramethylene glycol dimethacrylate, polytetramethylene glycol diacrylate, diallyl maleate and diallyl phthalate.

Propellants of the invention without cross-linking agents directly incorporated therewith are particularly advantageously applied in the case of a small diameter end burner, in which low stress would be brought on either the propellant mass or the case bonding system.

Any suitable supplemental oxidizing ingredientcan be employed. Of the preferred supplemental oxidizers, proportions of nitrocellulose up to as high as 15 weight percent can be utilized, nitroglycerin proportions up to about 50 percent being advantageously employed. Further exemplary of supplemental oxidizing agents in the practice of the invention are: glycerol dinitrate, triglycerol dinitrate, diglycerol dinitrate, glycol dinitrate, petrin, trinitroethyl nitrate, erythritol tetranitrate, trinitroethyl orthocarbonate, bis-trinitroethyl carbonate, bis-trinitroethylarnine, bis-trinitroethylurea and trinitrotriazidobenzene.

Further exemplary of polymerization catalysts employed in the practice of the invention are: alkyl and aryl peroxides, alkyl and aryl hydroperoxides, alkyl and aryl peroxyesters, and azo alkyl nitriles; and illustrative specific catalysts including t-butyl hydroperoxide, dicumyl peroxide, azodiisobutyronitrile, azoacetic ester, diazomethane, benzoyl propionyl peroxide, t-butyl peracetate, p-chlorobenzoyl peroxide, peracetic acid and perbenzoic acid.

Illustrative of solvents that can be employed to serve as plasticizers of the cured propellant in the practice of the invention are: organic esters such as alkyl and aryl acetates, butyrates, benzoates, and salicylates; organic ethers such as dialkyl, alkyl-aryl and aryl; alkyl and aryl phosphates; and alkyl and aryl sulfones. Illustrative of specific plasticizer compounds are: dibutyl phtnalate, din-propyl adipate, dibutyl maleate, octyl benzoate, pentaerythritol tetraacetate, pentaerythritol acetate-propionate, butyl pnthalylethyl glycollate, polyethylene, glycol acetates, polyethylene glycol benzoates, tributyl phosphate, sucrose octaacetate, ethylene carbonate, butyl lactate, diglycol levulinate, diglycol diacetate, dihexyl furnarate, dihexyl succinate, N-substituted derivatives of acrylarnide, e.g., dinitrato-n-propyl acrylamide, petrin xy acrylic acid and petrin oxy diethylene glycol acrylate.

Generally, less than about 20 weight percent of such solvent is employed, more often from about 5 to 10 percent. Use of a plasticizer solvent is dispensed with when possible inasmuch as it does not supply energy and thereby requires a sacrifice of the amount of net energy in the propellant.

The plateau burning rate of the propellants of this invention can be regulated, or modified, in order to regulate pressure generated by burning the propellant substantially constant over prolonged periods. When this result is obtained, the slope n of the line representing the pressure-burning rate relationship of the propellant must approach about in the zone of useful rocket pressure. Selected lead compound modifiers, as illustrated, and

pounds of lead and aliphatic compounds of lead. Those lead compounds of the above said copending applications which are soluble in the monomeric petrin ester are employed in the practice of the invention, when such modifier is required. Particularly preferred soluble (in the ester monomer) modifiers are lead acetylsalicylate and lead ,B-methoxypropionate.

The propellant compositions, and their preparation, are illustrated with reference to the following examples.

XAMPLE I Petrin was prepared frompentaerythritol and a mixture of HNO and H SQ adjusted to preferentially form the trinitrate. Minor amounts of dinitrate and tetranitrate were eliminated by extracting the reaction mixture with methylene chloride and evaporating to give essentially pure petrin with a little dissolved tetranitrate. The latter was precipitated by cooling and removed by filtration. The petrin had a nitrogen content of 15.5% N (theoretical 15.48% N).

The petrin was converted by treatment with acrylyl chloride to the acrylate which was purified by recrystallization from ethanol. Pctrin acrylate melts at 78 C., and shows excellent heat stability at 110 C. in the Taliani test and at 82 C. in the Kl test. Its heat of explosion is about 770 caL/g.

Ingredients of the propellant of Example I of Table 1 except that the petrin ester was monomeric, were formed into a true solution and cast in the proportion shown. After curing at 65 C. for 48 hours, during which time the monomeric petrin ester was polymerized, the strands of the cured propellant were burned under nitrogen pressure to give burning rates shown for Example I in Table 1.

EXAMPLE H Petrin prepared as in Example I was converted by treatment with methacrylyl chloride to the methacrylate and purified by recrystallization from ethanol. Petrin methacrylate melts at C. It has excellent heat stability at 110 C. in the 'laliani test and at 82 C. in the Kl test. Its heat of explosion is about 700 ca1./ g. Ingredients of the propellant of Example II, Table l, were mixed and cast. After curing at C. for hours, strands of the cured propellant were burned under nitrogen pressure to give the binning rates shown for Example H in Table I.

Table 1 Example No Petrin aerylato polymer Petrin methacryate polymer Nitroglycerin Petrin Diglyeol dimethacrylate. Diglycol diacetate Lead acetylsalieyl- Benzoyl peroxide Heat of explosion (caL/g.) Burning rate at 800 psi. (in/sec.)

850 p.s ./sec.) 1200 p. (in/sec) 1300 p in./see.)

1600 p:s.1. (ind/sec.) 1650 psi. (in/sec 1800 psi. (in/see.)

' Methyl mothacrylate to copolyrnerize with petrin acrylate.

as disclosed and claimed in my copending applications Serial Nos. 492,802, now Patent No. 3,033,715, and 492,801, now Patent No. 3,033,716, each filed March 7, 1955, can be utilized in the regulation of the burning rate to give a slope for the burning rate-pressure curve at a value approaching 0 over a prolonged period. These compositions can, therefore, be so modified and referred to as platonic propellants. Lead modifiers as set forth in the above referred to copending applications are aromatic compounds of lead, lead, inorganic comsuch as small turbo-electric generators or turbo-mechani- V cal pumps, etc.

Thermostability of the compositions is high over prolonged periods so as to make these compositions particularly suitable for high temperature casting and for high temperature storage over prolonged periods. Thus, relatively 'high use temperatures can be tolerated. For example, actual soak temperatures in the order of 250- 300" 'F. can be employed.

The propellant compositions of this invention, prepared by solution casting, curing and polymerization, as described above, by virtue of the polymeric petrin ester component, particularly when cross-linked as above described, are generally stronger and harder than conventional solid double base propellants of the prior art and exhibit improved resistance to cold flow. These improved strength and hardness characteristics are a function of the content of total polymer in the system which can be greater than that possible when the acrylate or methacrylate is originally cast in polymeric form. These improved strength and hardness characteristics also result from the polymer knitting of the acrylic chains as result of the in situ polymerization, whereas When the already polymerized petrin ester ingredient is added to the casting system, the individual polymer particles in the cured composition can only adhere to one another or through intermediary particles by cohesive forces, in which event any improved strength and elongation in the system is supplied by other polymer. These differences are particularly great when the polymer is cross-linked in each instance. By way of further example, a propellant prepared in accordance with the solution casting method of this invention and which contains cross-linked petrin ester polymer ingredient and is characterized by elongation (percent), tensile strength (psi) and cold flow (percent elongation after 16 hours at 1 psi, load) of 30,110 and 2.5, respectively, would have had corresponding values in the order of 10, 40 and flow had the same cross-linked polymer been initially added to the casting system, i.e., employing no in situ polymerization. Similarly, the same propellant prepared utilizing the in situ polymerization except no cross-linking agent was utilized in the casting system, would be characterized by respective elongation, tensile and cold flow values of 60, 95 and 5, whereas with the same uncross-linked polymer initially added to the casting system, i.e., no in situ polymerization, would have had respective values in the order of 40, 7 and 8;

Although the monomeric petrin acrylic ester can be polymerized to a molecular weight as high as, say about 500,000, as measured by intrinsic viscosity, in general, the maximum average molecular weight of the polymerized ester will be in the order of about 100,000-150,000 measured as above described. Although higher molecular Weights can be utilized, say up to about 1,000,000, those values are generally not preferred because insufficient im provement in physical properties is attained to Warrant the increased manufacturing difficulties associated with attaining the higher molecular weight.

Monomeric petrin acrylate and methacrylate'oxidizer components of the propellants of the invention canbe prepared in accordance with any suitable procedure. However, they are=conveniently prepared by direct nitration of pentaerythritol to 'form the trinitr-ate followed by esterification of the resulting ester to form the acrylate or methacrylate as the case may be as illustrated herein.

The propellants of this invention are suitably case bonded directly to a prepared metal surface, e.g., which has been simply sand blasted and degreased. In most instances, however, motor chambers utilize an intermediate case bonding lacquer, or plastic liner, on the metal surface, e.g., a cellulose acetate lacquer cross-linked with toluene diisocyanate. In such instances a particularly strong bond of propellant to plastic liner is obtained when solution casting in such a lined motor chamber in the practice of the invention, bond strength, i.e., propellant to liner, being in the order of about 50 to 70 psi. and higher as compared with strengths in the order of 10 to 20 psi. when no acrylate formulations are employed or when the acrylate is polymerized prior to casting. These improved case bonding characteristics are due to the extension of the polymeric 'petrin acrylate ingredients from the plastic propellant body into the plastic liner, which is accomplished as result of the method of this invention whereby monomeric petrin acrylate ester in the casting system is permitted to penetrate from the solution into the plastic chamber liner and to then polymerize during curing to provide for a continuous bridging type bond between the propellant and the chamber. liner.

Incorporation of the monomeric petrin acrylic ester into the propellant, for casting, followed by curing and polymerization, is an important feature of the invention inasmuch as this provides for a simplified handling of the casting ingredients, and the bridging effect that takes place with concomitant continuous distribution of polymer from the propellant into the inhibitor provides for case bonding considerably stronger than that which would be obtained had the ester been introduced into the mold in polymeric form. The use of a plastic liner, or inhibitor as it is often called, in conjunction with introduction of the ester ingredient into the solution in polymeric form likewise results in case bonding inferior to that obtained when the ester ingredient is introduced in monomeric form into the mold to form the above described bridging effect.

As will be evident to those skilled in the art, various modifications can be made, or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims,

What I claim and desire to protect by Letters Patent 1. In the manufacture of a solid rocxet propellant, the improvement comprising forming said propellant by admixing, at a temperature not exceeding 70 C., from about 30-95 percent of at least one liquid monomeric ester selected from the group consisting of an acrylate and a methacrylate of pentaerythritol trinitrate, with from 0.1 percent to 2 percent each of a stabilizer ingredient for said propellant and a catalyst capable of promoting polymerization of said monomeric ester, and with at least one remaining ingredient for said propellant selected from the group consisting of 1-10 percent of an olefinically unsaturated monomer copolymerizable with said monomeric ester, from ll0 percent of a cross-linking comonomer copolymerizable with said monomeric ester to provide a resulting branched chain polymeric ester, from l050 percent of a supplemental oxidizer ingredient, at least 5 percent but less than about 20 percent of a plasticizer compound, and a suificient amount of a lead compound selected from the group consisting of lead acetylsalicylate, and lead fi-methoxypropionate for regulating the burning rate and pressure relationship of said propellant so that the slope n of the line representing the said relationship will approach zero in the zone of useful rocket pressure, each of said catalyst, stabilizer and remaining ingredients so admixed with said mono meric ester being soluble therein to form a true solu tion, maintaining the resulting solution at a temperature not exceeding about C. for a time sufiicient to at least partially polymerize said monomeric ester to form said solid propellant, and the above said proportions of propellant ingredients being based on the weight of the said propellant so produced.

2. In a method of claim 1, disposing the said solution of propellant ingredients in a chamber of a rocket motor and therein heating same, as described, to form said solid propellant.

3. A method of claim 2 wherein said chamber contains a plastic layer adhered to. its inner wall as a liner therefor, wherein monomeric ester migrates from said solution into said plastic liner, and wherein upon heating said solution to form said solid propellant, as described, a continuous bridging bond of polymeric ester extends from the solid propellant product into said liner.

4. A method of claim 1 wherein said monomeric ester is the said acrylate.

5. A method of claim 1 wherein said monomeric ester is the said methacrylate.

6. A method of claim 3 wherein said solution is maintained in said chamber in contact with said liner at a temperature in the range of from 60 to 75 C. for a period of from 40 to 100 hours to form said solid propellant.

7. A method of claim 1 wherein said solution is maintained under said conditions for polymerizing the monomeric ester for a time sufiicient to form a resulting polymeric ester having a molecular weight in the order of from about 100,000 to 150,000 as measured by intrinsic viscosity.

8. A solid rocket propellant formed by admixing from about 30-95 percent of at least one liquid monomeric ester selected from the group consisting of an acrylate and a methacrylate of pentaerythritol trinitrate, with from 0.1 percent to 2 percent each of a stabilizer ingredient for said propellant and a catalyst capable of promoting polymerization of said monomeric ester, and with at least one remaining ingredient for said propellant selected from the group consisting of 1-10 percent of an olefinically unsaturated monomer copolymerizable with said monomeric ester, from 1-10 percent of a cross-linking comonomer copolymerizable with said monomeric ester to provide a resulting branched chain polymeric ester, from 10-50 percent of a supplemental oxidizer ingredient, at least 5 percent but less than about 20 percent of a plasticizer compound, and a sufficient amount of a lead compound selected from the group consisting of lead acetylsalicylate, and lead B-methoxypropionate for regulating the burning rate and pressure relationship of said propellant so that the slope n of the line representing the said relationship will approach zero in the zone of useful rocket pressure, each of said catalyst, stabilizer and remaining ingredients so admixed with said monomeric ester being soluble therein to form a true solution, maintaining the resulting solution at a temperature not exceed ing about 75 C. for a time sufl'icient to at least partially polymerize said monomeric ester to form said solid propellant, and the above said proportions of propellant ingredients being based in the weight of the said propellant so produced.

9. A propellant of claim 8 containing diglycol diniethacrylate utilized as a cross-linking agent.

10. A propellant of claim 8 containing divinyl benzene utilized as a cross-linking agent.

11. A propellant of claim 8 wherein glycol diacrylate has been utilized as a cross-linking agent.

12. A rocket propellant of claim 8 containing up to 15 percent nitrocellulose as a supplemental oxidizer.

13. A rocket propellant of claim 8 containing nitroglycerin as a supplemental oxidizer.

14. A propellant of claim 8 wherein said catalyst utilized is benzoyl peroxide.

15. As a new article, a rocket motor, a layer of plastic material adhered to the inner wall of the chamber of said motor as a liner therefor, a solid propellant contained within said chamber in direct contact along its entire non-burning surface with said liner and a continuous bridging bond of polymer extending from said propellant into said liner, said propellant and the above said bond of polymer being formed by admixing from about 30-95 percent of at least one liquid monomeric ester selected from the group consisting of an acrylate and a methacrylate of pentaerythritol trinitrate, with from 0.1 percent to 2 percent each of a stabilizer ingredient for said propellant and a catalyst capable of promoting polymeriztaion of said monomeric ester, and with at least one remaining ingredient for said propellant selected from the group consisting of 1-10 percent of an olefinically unsaturated monomer copolymerizable with said monomeric ester, from 1-10 percent of a cross-linking comonomer copolymerizable with said monomeric ester to provide a resulting branched chain polymeric ester, from 10-50 percent of a supplemental oxidizer ingredient, at least 5 percent but less than about 20 percent of a plasticizer compound, and a sutficient amount of a lead compound selected from the group consisting of lead acetylsalicylate, and lead fl-methoxypropionate for regulating the burning rate and pressure relationship of said propellant so that the slope of n of the line representing the said relationship will approach zero in the zone of useful rocket pressure, each of said catalyst, stabilizer and remaining ingredients so admixed with said monomeric ester being soluble therein to form a true solution, heating the resulting solution within said chamber at a temperature not exceeding about C. for a time suflicient to at least partially polymerize said monomeric ester to form solid propellant, migration of monomeric ester from said solution into said liner taking place prior to termination of said heating and monomeric ester so migrated becoming, during said heating, at least partially polymerized to provide the above said continuous bond of polymer extending from said propellant into said liner.

16. A motor of claim 15 wherein the resulting polymeric ester is characterized by a molecular Weight from about 100,000 to about 500,000 as measured by intrinsic viscosity.

17. A rocket motor assembly of claim 15 wherein said plastic liner is cellulose acetate lacquer cross-linked with toluene diisocyanate.

References Cited in the file of this patent UNITED STATES PATENTS 2,740,702 Mace Apr. 3, 1956 2,783,138 Parsons Feb. 26, 1957 2,852,359 Achilles Sept. 16, 1958 OTHER REFERENCES Deschere: Ind. Eng. Chem, vol. 49, No. 9, September 1957, pp. 1333-6.

Zaehringer: Missiles and Rockets, vol. 4, No. 6, Aug. 11, 1958, pp. 28, 9, 31-4, and 37. 

15. AS A NEW ARTICLE, A ROCKET MOTOR, A LAYER OF PLASTIC MATERIAL ADHERED TO THE INNER WALL OF THE CHAMBER OF SAID MOTOR AS A LINER THEREFOR, A SOLID PROPELLANT CONTAINED WITHIN SAID CHAMBER IN DIRECT CONTACT ALONG ITS ENTIRE NON-BURNING SURFAE WITH SAID LINER AND A CONTINUOUS BRIDGING BOND OF POLYMER EXTENDING FROM SAID PROPELLANT INTO SAID LINER, SAID PROPELLANT AND THE ABOVE SAID BOND OF POLYMER BEING FORMED BY ADMIXING FROM ABOUT 30-95 PERCENT OF AT LEAST ON LIQUID MONOMERIC ESTER SELECTED FROM THE GROUP CONSISTING OF AN ACRYLATE AND A METHACRYLATE OF PENTAERYTHRITOL TRINITRATE, WITH FROM 0.1 PERCENT TO .2 PERCENT EACH OF A STABILIZER INGREDIENT FOR SAID PROPELLANT AND A CATALYST CAPABLE OF PROMOTING POLYMERIZATION OF SAID MONOMERIC ESTER, AND WITH AT LEAST ONE REMAINING INGREDIENT FOR SAID PROPELLANT SELECTED FROM THE GROUP CONSISITNG OF 1-10 PERCENT OF AN OLEFINICALLY UNSATURATED MONOMER COPOLYMERIZABLE WITH SAID MONOMERIC ESTER, FROM 1-10 PERCENT OF A CROSS-LINKING COMONOMER COPOLYMERIZABLE WITH SAID MONOMERIC ESTER TO PROVIDE A RESULTING BRANCHED CHAIN POLYMERIC ESTER, FROM 10-50 PERCENT OF A SUPPLEMENTAL OXIDIZER INGREDIENT, AT LEAST 5 PERCENT BUT LESS THAN ABOUT 20 PERCENT OF A PLASTICIZER COMPOUND, AND A SUFFICIENT AMOUNT OF A LEAD COMPOUND SELECTED FROM THE GROUP CONSISTING OF LEAD ACETLYSALICYLATE, AND LEAD B-METHOXYPROPIONATE FOR REGULATING THE BURNING RATE AND PRESSURE RELATIONSHIP OF SAID PROPELLANT SO THAT THE SLOPE OF N OF THE LINE REPRESENTING THE SAID RELATIONSHIP WILL APPROACH ZERO IN THE ZONE OF USEFUL ROCKET PRESSURE, EACH OF SAID CATALYST, STABILIZER AND REMAINING INGREDIENTS SO ADMIXED WITH SAID MONOMERIC ESTER BEING SOLUBLE THEREIN TO FORM A TRUE SOLUTION, HEATING THE RESULTING SOLUTION WITHIN SAID CHAMBER AT A TEMPERTURE NOT EXCEEDING ABOUT 75*C. FOR A TIME SUFFICIENT TO AT LEST PARTIALLY POLYMERIZE SAID MONOMERIC ESTER TO FORM SOLID PROPELLANT, MIGRATION OF MONOMERIC ESTER FROM SAID SOLUTION INTO SAID LINER TAKING PLACE PRIOR TO TERMINATION OF SAID HEATING AND MONOMERIC ESTER SO MIGRATED BECOMING, DURING SAID HEATING, AT LEAST PARTIALLY POLYMERIZED TO PROVIDE THE ABOVE SAID CONTINUOUS BOND OF POLYMER EXTENDING FROM SAID PROPELLANT INTO SAID LINER. 